Method for treating molten metal



Feb. 24, 1959 B. M. s. KALLING METHOD FOR TREATING MOLTEN METAL Filed June 11, 1956 United States PatetitO METHOD FOR TREATING MOLTEN METAL Bo Michael Sture Kalling, Domnarvet, Sweden,.assignor to Stora Kopparbergs Bergslags Aktiebolag, Falun, Sweden Application June 11, 1956, Serial No. 590,620 Claims priority, application Sweden June 15, 1955 7 Claims. (CI. 75-45) This invention relates to a method for the refining of metal melts, and particularly to a method to obtain an effective stirring action when treating a metal melt with a solid, liquid or gaseous refining agent.

It is often difficult by metallurgical processes to obtain a sufiiciently fast reaction due to inadequate stirring of the molten bath. This is particularly applicable if the process is carried out in a stationary furnace. In case the process itself fails to provide the necessary stirring action, as e. g. the blast air injection in the Bessemer process or the boiling in the open furnace process, but the stirring action has to be achieved by means of an external movement of the bath diflicult problems often arise, mainly due to the high temperature which is normally used for metallurgical processes prevents use of stirring apparatuses that are to be dipped into the bath.

Several principles have been previously proposed to activate the bath without use of stirring apparatuses. It is, for instance, possible to carry out the process in a rotary furnace with a horizontal shaft. Thereby a very intense mixing action may be obtained, particularly if the rate of rotation is maintained high (see c. g. Swedish Patents Nos. 135,751 and 137,382). A rotary furnace is, however, comparatively expensive and inconvenient. It is, of course, an improvement to carry out the reaction in a vessel or ladle, which is rotated around a vertical shaft, e. g. by placing it on a rotating table. In this case, however, the mixing action will be considerably less as the melt follows the vessel during the rotation and quickly attains a state of equilibrium within the vessel without being moved, at least as long as the rate of rotation is constant. A more effective stirring action may be obtained by an electrodynamic process, a method that inter alia has been used for electrical steel manufacture. In this case the melt is circulated in a stationary furnace, whereby the bath obtains an intense motion with respect to the furnace, which will increase the stirring action considerably due to the friction between the melt and the furnace lining.

The present invention relates to a method for the refining of metal melts wherein the melt mechanically is powerfully moved relative to the wall of the vessel. The method according to the invention is characterised in that the reaction vessel containing the metal melt without rotation is moved along a substantially circular path with respect to a substantially vertical axis, the speed of the reaction vessel and the radius of said path thereby being regulated so that the metal melt performs a circular motion within the vessel, and in that a refining agent is added to the metal melt prior to or during the treatment.

The invention will be explained hereinafter with reference made to the accompanying drawing, illustrating in vertical section one embodiment of an apparatus to carry out the method according to the invention.

The apparatus according to the drawing comprises a table 1, adapted to support a furnace, ladle or another vessel 7, containing the bath which is to be treated.

The table is supported in known manner on a disc 2, which in turn is adjustable with respect to a lower table 5 by means of an adjustable eccentric ring 3. The table 5 is rotatable around a fixed axis 4 and arranged to be driven at the desired speed from a shaft 8. The upper table 1, which supports the vessel 7, is simultaneously guided at one point 6 in order to prevent the table 1 from rotating with respect to the axis 4. The vessel also may be guided by means of a mechanism identical with the one above described and driven at the same speed. In this case the table may be bigger, and, at the same time, space may possibly be accessible for several vessels.

The bath in the vessel 7 will be put into a circular motion or rotating wave motion by means of the mechanism described, and an effective mixing will be obtained by the friction against the walls of the vessel, the intensity of the mixing being determined in part by the eccentricity and in part by the rate of rotation of the table 5.

'The method according to the invention may be used for several metallurgical reactions where an. eifective mixing is valuable, but is particularly advantageous for certain processes, which are carried out at such a high temperature that normal mechanical stirring apparatuses are out of question. Particularly for sulphur refining of crude iron and for malleablising of crude iron with oxygen this new method has opened wide possibilities.

Sulphur refining of crude iron advantageously may be performed by treating the molten crude iron with solid pulverisedlime which maintains its pulverous state during the whole process. However, an intense mixing will be required during the treatment in order to obtain a rapid and complete reaction. Hitherto, this normally has been achieved by carrying out the process in a fast rotating furnace with a horizontal shaft (Swedish Patent No. 135,751). It may be a simpler and cheaper way to carry out the process according to the present invention. It is not necessary, then, to use a special furnace for the process. Instead it is possible to use a normal crude iron ladle, which, after charge of the crude iron and admixture of the necessary amount of lime, is placed on the eccentric table, which is rotated for some minutes, Whereafter the treatment is finished. The ladle should be well sealed during the process and, therefore, it is preferably provided with an insulated cover. In this manner a sulphur refining of utmost elficiency and quickness may be obtained.

Of course, the method may be used for sulphur refining of crude iron according to other methods, e. g. through admixture of soda into the ladle, whereby a liquid slag will be obtained on the crude iron surface. Also with this method the result is highly dependent on the mixing action which may be obtained in order to accelerate the reaction between the formed slag and the crude iron.

The method may also be used for phosphorous refining of crude iron, which may take place with very iron rich slags.

As mentioned above the method according to the invention also advantageously may be used for malleablising of crude iron with pure oxygen or air, enriched to a high oxygen content. If the oxygen content of the gas exceeds about 50% it is not possible to use the normal Bessemer process with air injection from the bottom, but the oxygen has to be blown in from above against the bath or into the same. This process, however, has certain difiiculties, due to the inadequate mixing if the process is carried out in a normal converter or another stationary furnace. Thus, the iron loss in the slag will be relatively high, particularly when it is desired to reduce' the phosphorous centent satisfactorily 3 when starting from a phosphorous rich crude iron, and further, there arises a considerable evaporation of iron due to the strongly localised "oxygen admission. It has been found possible. to avoid these disadvantages by using a horizontal rotary furnace for the process, but often the same advantage may be achieved in a simpler manner by use of a furnace which is moved according to the invention thereby. Another great advantage is the increasing of the bath surface which will be achieved by the movement according to the invention, whereby the contact with the oxygen may take place over a wide surface.

The method according to the invention is by no means limited to the treatment of crude iron but, of course, it may also be used for the treatment of other melts, e. g. for the refining of steel melts from carbon, sulphur and phosphorous, or for the treatment of melts of non-ferrous metals.

I claim:

1. A method for treating molten metal in a reaction vessel, comprising moving the vessel without rotation along a substantially circular path with respect to a substantially vertical axis, controlling the speed of the vessel so that the molten metal performs a circular motion within the vessel, and adding a treating agent to the molten metal in the vessel.

2. A method according to claim 1, characterised in that the metal melt is crude iron.

3. A method according to claim 1, characterised in that the treating agent is admixed in a solid state.

4. A method according to claim 3, characterised in that the treating agent is pulverised lime.

5. A method according to claim 1, characterised in that the treating agent constitutes a liquid phasein the reaction vessel. p

6. A method according to claim 1, characterised in that the treating agent is admitted to the reaction vessel in a gaseous state.

7. A method according to claim 6, characterised in that the treating agent is oxygen enriched air.

References (Iited in the file of this patent UNITED STATES PATENTS Rinesch Apr. 10, 1956 

1. A METHOD FOR TREATING MOLTEN METAL IN A REACTION VESSEL, COMPRISING MOVING THE VESSEL WITHOUT ROTATION ALONG A SUBSTANTIALLY CIRCULAR PATH WITH RESPECT TO A SUBSTANTIALLY VERTICAL AXIS, CONTROLLING THE SPEED OF THE VESSEL SO THAT THE MOLTEN METAL PERFORMS A CIRCULAR MOTION WITHIN THE VESSEL, AND ADDING A TREATMENT AGENT TO THE MOLTEN METAL IN THE VESSEL. 